Three Rivers Protection and Overflow Reduction Tunnel (3RPORT)

Fort Wayne, Indiana, USA

Environment Water Tunnel.

Project

The 3RPORT tunnel is part of the Long-Term Control Plan (LTCP) of the City of Fort Wayne (Indiana, USA) having the main goal to reduce the discharge of untreated Combined Sewer Overflows (CSO) and improve water quality in Fort Wayne’s CSO-impacted streams. The tunnel will have a length of 24’500 ft (7’480 m), an internal diameter of 16 ft (4.87 m) and will be excavated by means of a Herrenknecht slurry shield TBM with boring diameter 19 ft (5.81 m) and designed to operate with a support pressure of up to 6.5 bar. The 3RPORT tunnel is anticipated to be fully operational by the end of 2022 and the relief sewer by the end of 2025.

Due to the presence of open vertical and horizontal discontinuities, the hydraulic conductivity is expected to be extremely high, making the management of the water inflow during advance and during standstill the most important challenge of the project. The expected water inflow during interventions under atmospheric conditions ranges between 857 gpm (195 m3/h) and 10’000 gpm (2’271 m3/h). The minimum support pressure needed for compensating the undisturbed ground water pressure ranges from 5.2 bar to 6.2 bar.